Something you didn't mention is that highly aggressive men either self select for dangerous work or aren't suited for anything else. Because they go off to die in wars, their reproductive opportunities obviously are diminished. Less aggressive, more congenial men pursue less dangerous jobs which they secure by networking. This gives them the same high pay but much lower rates of premature death.
The result has been what you might call "self-domestication". Evolution has forced us into the shape needed to navigate complex social politics and manage stress without becoming aggressive.
Probably our plains dwelling ancestor would regard the modern man in the way that a wild wolf regards a golden retriever.
Look into the Flynn effect btw, it contradicts claims of overall cognitive decline.
I do think cognitive potential has not been in decline. Perhaps it has just been so overwhelmed with focusing on many things that at one time would be trivial. Whether it is watching and betting on sports, playing video games, going to the movies, etc. We are increasingly distracted by our own worlds we create. You as a writer are likely aware of this and have been for a long time. I also make games, and at times had said the only negative is that to a degree it can be much like pedaling a new drug. It can be subjectively argued that is may not be damaging, but I still ponder such things as I create.